Electrical screw terminals, normally as part of a terminal block, provide a versatile and reliable method of making electrical connections. The quality of the connection to a screw terminal, both in terms of providing low electrical resistance and high mechanical stability, is increased by increasing the clamping force of the nut on the wire. Increased clamping force may be obtained by applying greater torque to the machine screw. However, known screw terminals and terminal blocks are limited with respect to how much screw tightening torque they can accept and are correspondingly limited with respect to how much clamping force the screw terminals can apply to a wire.
In a simple terminal block, each screw terminal includes an electrically conductive machine screw which is threadably received by the terminal body. The wire to be connected is captured under the head of the machine screw as the machine screw is tightened.
In these simple terminal blocks, tightening the screw beyond a certain extent can squeeze the wire at least partially out from under the screw head. For multi-strand wires, this may reduce the number of strands that are mechanically held by the screw and compromise the electrical connection between the wire and screw terminal. For single-strand wires, this may completely remove the wire from its connection with the screw terminal, requiring an installer to loosen the screw and start over with connecting the wire to the terminal.
More sophisticated screw terminals employ enclosed channels into which the wire may be inserted to be captured between one wall (a clamping wall) of the channel and a threaded nut within the channel. Multiple terminals of this type may be held in an electrically insulating housing having barrier walls between terminals to form a terminal block. The nut may be guided by flanking walls of the channel to prevent its rotation as the machine screw is loosened or tightened. The channel may provide a lip opposite the clamping wall to retain the nut on the machine screw when the nut is loosened.
All such potential issues associated with existing screw terminals can compromise the clamping force that is applied to the wires and correspondingly compromise the integrity of the electrical connection. This can lead to device malfunction that may require field service calls by technicians to resolve and/or other downsides.